Laser apparatus

ABSTRACT

According to the present invention there is provided a laser apparatus capable of efficient oscillation with an excitation power source with comparatively low frequency, wherein discharge is obliquely generated within the rectangular section of a discharge space. There is also provided a laser apparatus with a pair of preliminary discharge excitation electrodes which can readily initiate discharge. There is further provided a laser apparatus capable of efficient oscillation with an excitation power source with comparatively low frequency, wherein provided is a pair of discharge excitation electrodes located in the major side direction of discharge space whose length is more than three times as long as that of minor side direction thereof. There is further provided a laser apparatus with a pair of discharge excitation electrodes whose dimension is smaller than that of a pair of dielectric plates, which apparatus can prevent undesirable discharge. There is also provided a laser apparatus with more than three discharge spaces at least one of which is given a lower electric field having the apparatus oscillate efficiently. There is further provided a laser apparatus with an improved oscillation efficiency wherein furnished are dielectric double pipes creating a substantially large discharge space.

This application is a divisional of application Ser. No. 08/007/231,filed Jan. 21, 1993 now U.S. Pat. No. 5,373,528.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a gas laser apparatus which is improved inoscillation efficiency.

2. Prior Art

FIG. 69 is a perspective view showing a conventional carbon dioxidelaser apparatus of the wave guide type disclosed, for example, in R.Nowack et al., "High Power CO₂ Wave Guide Laser of the 1 kW Category",SPIE (Society of Photooptical Instrumentation Engineers), Vol. 1276,Proceedings, "CO₂ Lasers and Application" (1990), pp. 18-28, FIG. 1.Referring to FIG. 69, reference numerals 1 and 2 each denote a dischargeexciting metal electrode. Reference numeral 3 denotes an excitationpower source (radio frequency power source here) connected to the metalelectrode 1. Reference numerals 10 and 20 denote dielectric plates madeof, for example, ceramics. The dielectric plates 10, 20 are opposite toeach other and held in close contact with the metal electrodes 1 and 2,respectively. Reference numeral 4 denotes a discharge space (filled withmixture gas of CO₂ --He--N₂ which serves as a laser medium) definedbetween the dielectric plates 10 and 20. Reference numerals 5 and 6denote arrow marks indicating the directions of coming in and going outof electrode cooling water to and from the electrodes, respectively.Reference numeral 7 denotes a total reflection mirror (resonatormirror). Reference 8 denotes output coupler (resonator mirror).Reference numeral 9 denotes a laser beam, and reference characters 21aand 21b denote inlet and outlet ports, respectively, for electrodecooling water provided at the electrode 1 (similar inlet and outletports (not shown) for electrode cooling water are provided also at theelectrode 2).

Subsequently, the operation of the apparatus will be described. When themetal electrode 1 is connected to the RF power source 3 and the othermetal electrode 2 is connected to the ground, the RF discharge forexciting the laser is caused in the discharge space 4 filled with themixture gas described above. Thus, the discharge energy is convertedinto light energy by an optical resonator constituted of the totalreflection mirror 7 and the output coupler 8 and is outputted as a laserbeam 9 from the output coupler 8.

In a carbon dioxide gas laser, since the energy level at a low level ofthe laser is low, as the temperature of the gas rises, the low levelconcentration increases and the laser oscillation efficiency drops.Consequently, the cooling capacity of the laser gas makes a great factorwhich determines the laser oscillation efficiency. The ratio w/d betweenthe major side (length w) and the minor side (gap length d) of a sectionof the rectangular discharge space 4 is called aspect ratio, and fromthe point of view of cooling of the gas serving as a laser medium, it isdeduced that, when the aspect ratio is equal, the cooling capacity issimilar.

In particular, when the same power is thrown in, if the aspect ratio isequal, then the temperature of the gas is equal. Accordingly, in orderto throw in a high power and cool the gas sufficiently to raise thelaser oscillation efficiency, the aspect ratio should be set to a highvalue. In addition, for laser oscillation for which a high power densityis required, the minor side d should be set to a small value.

The cooling capacity for gas with respect to the length d of the minorside of the section of the rectangular discharge space 4 is shown inFIG. 70. In FIG. 70, a solid line indicates a power density at which thetemperature of the gas is 250° C. where the composition of the gas isHe--N₂ --CO₂ =80--10--10 (%; rate in volume, molar fraction). It can beseen from FIG. 70 that the cooling capacity for the gas rises as theminor side d decreases.

On the other hand, when the minor side (gap length) d is set to beshort, the loss a in the propagation process of the laser lightincreases. The propagation loss a of the EH_(nm) mode in the rectangularwave guide can be represented by the following formula. ##EQU1## wherein∥ represents the laser wavelength; ε and ε₀ represent the permitivitywith respect to the laser wavelength and the dielectric constant invacuum (0.8854×10⁻¹¹ CV⁻¹ m⁻¹); and u_(nm) represents the coefficientwith respect to the order of each mode.

FIG. 71 shows the result obtained by calculating, from the aboveformulae, the relationship between the gap length d and the propagationloss a where Al₂ O₃ (alumina) is used for a dielectric material and awavelength (10.6 μm) of a carbon dioxide laser is used as a laserwavelength. As a result, the propagation loss a increases in proportionto the gap length d⁻³.

The normal wave guide type carbon dioxide gas laser apparatus is oftenused in the range of 1.5≦d≦2.5 (mm) in consideration of the coolingcapacity of gas and the propagation loss of light. Due to the highoutput, when the length of the dielectric is long, the propagation lossnaturally increases. Therefore, it is necessary to increase the gaplength d to provide a higher output.

FIG. 72 shows a result of an examination of the influence of the powersource frequency of the RF power source 3 upon the output of the carbondioxide gas laser in the condition of the gap length d=2 mm. It isconfirmed that, as the power source frequency increases, the laseroutput increases dramatically. The reason is given below.

FIG. 73 shows a result of calculation of the electric field distributionin the direction of the gap d varying the frequency of the power sourcein the condition of the gas pressure of 80 Torr. In FIG. 73, referencecharacter Z denotes a distance in the electric field direction, and Z=0represents the center of the gap while Z=1.0 (mm) represents a boundaryto a dielectric plate. As apparent from FIG. 73, it can be confirmedthat, as the power source frequency increases, the region in which theelectric field is high decreases while the low electric field regionwhich is suitable for laser oscillation increases. Accordingly, if thepower source frequency is raised, the low electric field regionincreases and the excitation efficiency of the laser rises as seen inFIG. 73.

This variation of the electric field distribution can be explained froma discharge maintaining mechanism. The discharge maintaining mechanismis roughly explained from the relationship between the travel time t_(e)of electrons through the gap d and the half period t_(s) of the powersource. In particular, in such a case that electrons drifting toward theanode collide with the anode (electrode), since the number of electronsand loss of energy are high, the electric field must provide the energywhich compensates for the loss. Accordingly, the high electric fieldregion becomes wide. This corresponds to the case wherein the halfperiod t_(s) of the power source is longer than the gap travel timet_(e) of electrons. On the contrary when the variation of the electricfield (half period t_(s) of the power source) is shorter than the traveltime t_(e) of electrons, the polarity of the electrode is reversed (tothe negative) before electrons drifting toward the anode arrive at theanode, and consequently, the electrons are urged back and will notcollide with the electrode wall. Accordingly, in this instance, the lossin the number of electrons and the energy loss are small and the highelectric field region may be made narrow.

Although it may be different depending upon conditions, in theconditions calculated in connection with FIG. 72, since the driftingspeed of electrons is almost 10⁷ cm/s, the gap travel time t_(e) is 0.2cm (2 mm)/10⁷ cm/s=2×10⁻⁸ sec. The critical frequency at which the timet_(e) corresponds to one half period of the RF power source 3 is 100MHz. Accordingly, when the frequency of the RF power source is lowerthan 100 MHz, the high electric field region becomes wide as shown inFIG. 73 and the lower excitation efficiency drops as shown in FIG. 72.

By the way, the conventional carbon dioxide gas laser apparatus shown inFIG. 69 employs a hybrid resonator in order to generate a laser beam ofhigh convergency from the rectangular discharge space 4. In particular,the hybrid resonator operates, in the direction of the minor side d ofthe rectangular discharge space 4, as a wave guide resonator in whichlaser light propagates while being reflected by the dielectric plates 10and 20, and operates, in the direction of the major side, as an unstableresonator (a resonator of the type in which light is not enclosedcompletely).

In the case where a wave guide is employed resonator, if the distance(L_(wm)) between an end of a wave guide (dielectric plates 10 and 20)and a resonator mirror (reflecting mirror 7 and output coupler 8) is setto a great value, then the rate at which light escapes from theresonator becomes high, and consequently, the output efficiency of alaser beam drops. It is known that the loss by escapement of lightincreases in proportion to (L_(wm))^(3/2). Thus, for example, in theconditions of the wave length of 10.6 μm (CO₂ laser) and the gap lengthof d=2 mm, in order to suppress the loss of light low, it is necessaryto set L_(wm) to a small value of 10 mm or so.

Accordingly, when the applied voltage is raised in order to increase thedischarge power, not only the discharge occurs in the main dischargespace 4, but also the discharge 41 toward the output coupler 8 occurs asseen in FIG. 74. In this instance, if the discharge occurs toward theoutput coupler 8, then the energy thrown in to the main discharge space4 decreases and the laser excitation efficiency drops as seen from FIG.75. (In FIG. 75, a point Ps denotes a discharge start power to themirror.)

Further, if corners of the dielectric plates 10 and 20 are present inthe proximity of end portions of the metal electrodes 1 and 2, then whenthe applied voltage rises, the electric field strengths at the cornersof the dielectric plates 10 and 20 become high as seen in FIG. 76, andthe discharge 42 is liable to be concentrated also at locations aroundthe corners.

Since the conventional laser apparatus is constructed as describedabove, in the case where the length of the dielectric is desired to belonger in order to obtain a high output wave guide type laser, it isrequired to set the gap length d to be short in view of cooling whereasit is required to set the gap length d to be long in view of propagationloss of light. This is exactly a contradictory requirement, which isimpossible to realize.

Further, if the permitivity ε with respect to the laser wavelength isset to be small from the above-described formulae (1) and (2), thepropagation loss a is expected to be reduced. Actually, however, amaterial having a low permitivity is difficult to be sintered, oftenmaking it impossible to manufacture.

As will be described later, the dielectric used in this system is notonly required to have a nature as a wave guide path surface but also tohave a function as a capacitor for discharge such as a withstandvoltage. For this reason, materials which satisfy with these conditionshave been extremely restricted.

Further, in the case of the conventional CO₂ laser apparatus, theoptimal frequency in the laser excitation is in the vicinity of 150 MHz.However, since this frequency is limited for use thereof under theJapanese Radio-wave Law, there remains a great problem in the case ofproviding a general-purpose apparatus. Moreover, such an RF power sourceis expensive, and matching between the RF power source and a laser loadis difficult. There are many problems as described.

Consequently, the conventional gas laser apparatus further has a problemthat, if the applied voltage is raised in order to increase thedischarge power, then not only does the discharge occur in the maindischarge space but also discharge 41 toward the resonator mirror anddischarge 42 concentrated at the corners of the dielectric plates occur,which deteriorates the stability of the laser apparatus.

SUMMARY OF THE INVENTION

The present invention has been made to eliminate such problems asdescribed above, and it is a principal object of the present inventionto provide a laser apparatus which can excite the laser readily at ahigh efficiency even in a frequency region approved, for example, by theradio wave law of Japan or in a low frequency region in which acountermeasure against radio wave leakage is easy.

It is another object of the present invention to provide a laserapparatus which can start the discharge smoothly.

It is a further object of the present invention to provide a stabilizedlaser apparatus which can suppress the discharge to an optical resonatormirror even upon application of a high voltage and concentration of thedischarge at a corner portion of a dielectric.

It is a still another object of the present invention to provide a laserapparatus which can minimize the light absorbing effect in a non-excitedand non-cooled space so that a laser can be outputted at a highefficiency even in a high output region.

It is another object of the present invention to provide a laserapparatus wherein laser light exciting spaces are formed and means isprovided to solidly turn back laser beams such as a prism, a holdingmirror and so forth, whereby when the laser light exciting spaces areconnected in series, the equal effects are obtained and the apparatuscan be miniaturized and provided at less cost.

It is another object of the present invention to provide a high-outputlaser apparatus which can minimize the propagation loss of light whilebeing satisfied with the conditions for discharge.

According to a first aspect of the present invention, there is provideda laser apparatus comprising a discharge space for laser excitationhaving a rectangular section of which ratio between a major side and aminor side is 3 or more and removing a laser beam in the directionintersecting perpendicularly to said rectangular section of saiddischarge space, characterized in that the discharge is generatedobliquely within the rectangular section of said discharge space.

According to a second aspect of the present invention, there is provideda laser apparatus comprising a discharge space for laser excitationhaving a rectangular section of which ratio between a major side and aminor side is 3 or more and removing a laser beam in the directionintersecting perpendicularly to said rectangular section of saiddischarge space, characterized in that the discharge is generatedobliquely with respect to the direction of an optical axis intersectingperpendicularly to said rectangular section within said discharge space.

According to a third aspect of the present invention, there is provideda laser apparatus comprising a discharge space for laser excitationhaving a rectangular section of which ratio between a major side and aminor side is 3 or more, removing a laser beam in the directionintersecting perpendicularly to said rectangular section of saiddischarge space, and generating a hot flow in the direction of the minorside of said rectangular section to cool gas, characterized in that aplurality of electrodes for discharge excitation are provided.

According to a fourth aspect of the present invention, there is provideda laser apparatus comprising a discharge space for laser excitationhaving a rectangular section of which ratio between a major side and aminor side is 3 or more, and removing a laser beam in the directionintersecting perpendicularly to said rectangular section of saiddischarge space, characterized in that a hot flow is generated in thedirection of the minor side of said rectangular section to cool gas, anda discharge is generated in the direction of the major side of saidrectangular section.

According to a fifth aspect of the present invention, there is provideda laser apparatus producing a discharge at a doughnut-like annularsection surrounded by an outer pipe and an inner pipe coaxiallydisposed, an inner periphery of said outer pipe and an outer peripheryof said inner pipe being utilized as wave guide paths for a laser beam,and removing a laser beam in the direction intersecting perpendicularlyto said annular section, characterized in that said outer pipe is formedfrom a dielectric, and two or more electrodes for applying analternating voltage are disposed in the outer periphery of said outerpipe.

According to a sixth aspect of the present invention, there is provideda laser apparatus producing a discharge at a doughnut-like annularsection surrounded by an outer pipe and an inner pipe coaxiallydisposed, an inner periphery of said outer pipe and an outer peripheryof an inner pipe being utilized as wave guide paths for a laser beam,and removing a laser beam in the direction intersecting perpendicularlyto said annular section, characterized in that said outer pipe is formedfrom a dielectric, and two or more electrodes for applying analternating voltage are juxtaposed in the direction of emitting saidlaser beam in the outer periphery of said outer pipe.

According to a seventh aspect of the present invention, there isprovided a laser apparatus comprising a discharge space for laserexcitation having a rectangular section of which ratio between a majorside and a minor side is 3 or more, and removing a laser beam in thedirection intersecting perpendicularly to said rectangular section ofsaid discharge space, characterized in that a hot flow is generated inthe direction of the minor side of said rectangular section, and gascooling means is provided to cool a laser gas in a non-discharge portionthrough which said laser beam passes.

According to an eighth aspect of the present invention, there isprovided a laser apparatus comprising a discharge space for laserexcitation having a rectangular section of which ratio between a minorside and a major side is 3 or more, and removing a laser beam in thedirection intersecting perpendicularly to said rectangular section ofsaid discharge space, characterized in that a metal electrode is set tobe shorter than a dielectric plate used as a reflection surface for alaser light, and a cooling pipe having a cooling function is disposedbetween a resonator mirror and the metal electrode in a state where thecooling pipe is electrically floated or grounded.

According to a ninth aspect of the present invention, there is provideda laser apparatus comprising a discharge space for laser excitationhaving a rectangular section of which ratio between a minor side and amajor side is 3 or more, and removing a laser beam in the directionintersecting perpendicularly to said rectangular section of saiddischarge space, characterized in that a cooling pipe for cooling alaser gas having an opening within three times of a diameter of a beamis disposed between a resonator mirror and a laser output window.

According to a tenth aspect of the present invention, there is provideda laser apparatus comprising a discharge space for laser excitationhaving a rectangular section of which ratio between a major side and aminor side is 3 or more and removing a laser beam in the directionintersecting perpendicularly to said rectangular section of saiddischarge space, characterized in that a hot flow is generated in thedirection of the minor side of said rectangular section to cool a lasergas, and a gas flow is forcibly generated in a non-discharge portionthrough which said laser beam passes to suppress a rise of a temperatureof said laser gas.

According to an eleventh aspect of the present invention, there isprovided a laser apparatus comprising a discharge space for laserexcitation having a rectangular section of which ratio between a majorside and a minor side is 3 or more, and removing a laser beam in thedirection intersecting perpendicularly to said rectangular section ofsaid discharge space, characterized in that gas cooling means isprovided to generate a hot flow in the direction of the minor side ofsaid rectangular section to cool a laser gas, gas-leakage preventiveside plates are provided on both sides of said discharge space, and alaser gas is suppled from substantially the central portion of said sideplates and evacuated in vacuum so that a gas pressure within saiddischarge space is substantially constant.

According to a twelfth aspect of the present invention, there isprovided a laser apparatus having a discharge space for laserexcitation, said discharge space being arranged so that linearsymmetrical axes are two or more, and removing a laser beam in thedirection intersecting perpendicularly to a section of said dischargespace, characterized in that the laser beam which passes through thesection of said discharge space is joined into one using solid beamturn-back means.

According to a thirteenth aspect of the present invention, there isprovided a laser apparatus having a rectangular discharge space whoseratio of length between a plurality of major sides and minor sides, thesection of said rectangular discharge space being arranged so thatlinear symmetrical axes are at least more than 2, and removing a laserbeam in the direction intersecting perpendicularly to said dischargespace section, characterized in that the laser beam which passes throughthe section of said discharge space is joined into one using solid beamturn-back means.

According to a fourteenth aspect of the present invention, there isprovided a laser apparatus having a rectangular discharge space of whichratio of length between a plurality of major sides and minor sides is 3or more, the section of said rectangular discharge space being arrangedinto a polygonal shape, and removing a laser beam in the directionintersecting perpendicularly to said discharge space section,characterized in that the laser beam which passes through the section ofsaid discharge space is joined into one using solid beam turn-backmeans.

According to a fifteenth aspect of the present invention, there isprovided a laser apparatus having a plurality of solid laser media, thesection of said solid laser media being arranged so that linearsymmetrical axes are at least two or more, and removing a laser beam inthe direction intersecting perpendicularly to the section of said solidlaser media, characterized in that heat is removed from the direction ofthe major side of said discharge space section to cool gas, and thelaser beam which passes through the section of said solid laser media isjoined into one using solid beam turn-back means.

According to a sixteenth aspect of the present invention, there isprovided a laser apparatus having a plurality of solid laser media, thesection of said solid laser media being arranged into a polygonal shape,and removing a laser beam in the direction intersecting perpendicularlyto the section of said solid laser media, characterized in that heat isremoved from the direction of the major side of said discharge spacesection, and the laser beam which passes through the section of saidsolid laser media is joined into one using solid beam turn-back means.

According to a seventeenth aspect of the present invention, there isprovided a laser apparatus of the discharge excitation waveguide pathtype which uses, as a light reflection surface, a dielectric formed of aplurality of materials which are different in the dielectric constant ofa laser light to a wavelength, characterized in that said dielectric onthe metal electrode side for discharge excitation is formed of amaterial having a high dielectric constant, and that on the dischargeplasma side is formed of a material having a low dielectric constant.

With the laser apparatus according to the first and second aspects ofthe present invention, since the discharge is caused in obliquedirections within the rectangular section of the discharge space, theeffective length of the gap can be set to be long, and for this reason,a proportion of a high electric field region for maintenance ofdischarge reduces, and an average electric-field intensity lowers toincrease a laser excitation efficiency.

With the laser apparatus according to the third aspect of the presentinvention, since a plurality of electrodes for discharge excitation areprovided, the effective length of the gap can be set to be long, and forthis reason, a proportion of a high electric field region formaintenance of discharge reduces, and an average electric-fieldintensity lowers to increase a laser excitation efficiency, similarly tothe case of the laser apparatus of the above-described first and secondaspects.

With the laser apparatus according to the fourth aspect of the presentinvention, the effective length of gap can be set to be long, and forthis reason, a proportion of a high electric field region formaintenance of discharge reduces, and an average electric-fieldintensity lowers to increase a laser excitation efficiency, similarly tothe case of the laser apparatus of the above-described first to thirdaspects.

With the laser apparatus according to the fifth and sixth aspects of thepresent invention, since an outer pipe is formed from a dielectric, anda plurality of electrodes for applying an alternating voltage aredisposed in the outer periphery of the outer pipe, a doughnut-likeannular portion is utilized as a discharge space, whereby the effectivelength of the gap becomes long. Thereby, a proportion of a highelectric-field region for maintenance of discharge reduces, an averageelectric-field intensity lowers, and a laser excitation efficiencyincreases.

With the laser apparatus according to the seventh to eleventh aspects ofthe present invention, a gas temperature does not rise in anon-excitation space where no inverse distribution is produced so thatthe coefficient of light absorption can be suppressed to a low value andthe efficiency for removing the laser increases.

With the laser apparatus according to the twelfth aspect of the presentinvention, since the effect equal to the case where a plurality of laserlight excitation spaces are connected in series is obtained, the laserbeams amplified in the respective laser light excitation spaces aresolidly turned back and joined into one to assume a state as if they areamplified in a single laser light excitation space. Accordingly, thelaser beam emitted from the laser apparatus is not plural but one, thusminimizing the apparatus and reducing the cost.

With the laser apparatus according to the thirteenth and fourteenthaspects of the present invention, a rectangular discharge space having alarge aspect ratio can be produced, and a cooling capacity for laser gascan be increased. Accordingly, the effect similar to that of theaforementioned twelfth aspect can be obtained.

With the laser apparatus according to the fifteenth and sixteenthaspects of the present invention, the laser beams are amplified in thesolid laser media spaces, and the amplified laser beams are solidlyturned back into one to assume a state as if they are amplified in asingle solid laser media space. Accordingly, the laser beam emitted fromthe solid laser apparatus is not plural but one, thus miniaturizing theapparatus and reducing the cost.

With the laser apparatus according to the seventeenth aspect of thepresent invention, for a dielectric layer for determining a fundamentalcharacteristics of discharge, a conventional material having a highdielectric constant and a high voltage resistance can be used withoutthe necessity of consideration of the propagation loss of light.Furthermore, since a waveguide path surface is formed of a materialhaving a low dielectric constant, a loss of a waveguide path is small.Accordingly, the propagation loss of light can be suppressed to a smallvalue even if a long dielectric is used, thus realizing a waveguide pathtype laser apparatus of high output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a gas laser apparatusaccording to an embodiment of the present invention;

FIGS. 2 and 3 are graphs each illustrating a relationship between thedischarge power and the laser output of the gas laser apparatus of FIG.1;

FIG. 4 is a schematic sectional view showing a gas laser apparatusaccording to another embodiment of the present invention;

FIG. 5 is a schematic sectional view showing a gas laser apparatusaccording to a further embodiment of the present invention;

FIG. 6 is a schematic sectional view showing a gas laser apparatusaccording to a still further embodiment of the present invention;

FIG. 7 is a perspective view showing a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 8 is a schematic sectional view showing a gas laser apparatusaccording to a yet further embodiment of the present invention;

FIG. 9 is a schematic illustration of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 10 is a graph illustrating a relationship between the dischargepower and the laser output of the gas laser apparatus of FIG. 9;

FIG. 11 is a schematic illustration of a gas laser apparatus accordingto a yet further embodiment of the present invention;

FIG. 12 is a schematic illustration of a gas laser apparatus accordingto a yet further embodiment of the present invention;

FIG. 13 is a schematic illustration of a gas laser apparatus accordingto a yet further embodiment of the present invention;

FIG. 14 is a schematic sectional view showing a gas laser apparatusaccording to a yet further embodiment of the present invention;

FIG. 15 is a circuit diagram showing an electrically equivalent circuitto the gas laser apparatus of FIG. 14;

FIG. 16 is a graph illustrating the thrown in power characteristic ofthe gas laser apparatus of FIG. 14;

FIG. 17 is a schematic illustration of a gas laser apparatus accordingto a yet further embodiment of the present invention;

FIG. 18 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 19 is a perspective view showing a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 20A is a plan view showing a gas laser apparatus according to a yetfurther embodiment of the present invention, and FIG. 20B is a sectionalview taken along line A--A of FIG. 20A;

FIG. 21A is a plan view showing a gas laser apparatus according to a yetfurther embodiment of the present invention, and FIG. 21B is a sectionalview taken along line A--A of FIG. 21A;

FIG. 22 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 23 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 24 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 25 is a perspective view showing a gas laser apparatus according toa yet further embodiment of the present invention;

FIGS. 26A and 26B are side elevational views showing manners of thedischarge when the applied voltage of the gas laser apparatus of FIG. 25is low and high, respectively;

FIG. 27 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 28 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 29 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 30 is a side elevational view of a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 31 is a perspective view showing a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 32 is a perspective view showing a gas laser apparatus according toa yet further embodiment of the present invention;

FIG. 33 is a perspective view of a laser apparatus according to anEmbodiment 27 of the present invention;

FIG. 34 is a graphic representation showing the laser oscillationcharacteristics of the laser apparatus shown in FIG. 33;

FIG. 35 is a graphic representation showing the laser oscillationcharacteristics of a conventional laser apparatus in comparison with thelaser apparatus shown in FIG. 33;

FIG. 36 is a graphic representation showing the relationship between thecoefficient of light absorption of carbon dioxide and the gastemperature in the laser apparatus;

FIG. 37 is a perspective view of a laser apparatus according to anEmbodiment 28 of the present invention;

FIG. 38 is a perspective view of a laser apparatus according to anEmbodiment 29 of the present invention;

FIG. 39 is a perspective view of a laser apparatus according to anEmbodiment 30 of the present invention;

FIG. 40 is a view showing a laser beam light path of the laser apparatusshown in FIG. 39;

FIG. 41 is a sectional view of a laser apparatus according to anEmbodiment 31 of the present invention;

FIG. 42 is a view showing a laser beam light path of the laser apparatusshown in FIG. 41;

FIG. 43 is a sectional view of the laser apparatus according to anEmbodiment 32 of the present invention;

FIG. 44 is a perspective view of the laser apparatus shown in FIG. 43;

FIG. 45 is a view showing a laser beam light path shown in FIG. 44;

FIG. 46 is a view showing the arrangement of a rectangular dischargespace of the laser apparatus according to an Embodiment 33 of thepresent invention;

FIG. 47 is a view showing a laser beam light path shown in FIG. 46;

FIG. 48 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 34 of the presentinvention;

FIG. 49 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 35 of the presentinvention;

FIG. 50 is a perspective view of a laser apparatus according to anEmbodiment 36 of the present invention;

FIG. 51 is a perspective view of a solid laser apparatus according to anEmbodiment 37 of the present invention;

FIG. 52 is a view showing the arrangement of a solid laser mediumaccording to an Embodiment 38 of the present invention;

FIG. 53 is a view showing the arrangement of a solid laser medium of asolid laser apparatus according to an Embodiment 39 of the presentinvention;

FIG. 54 is a perspective view of a solid laser apparatus according to anEmbodiment 40 of the present invention;

FIG. 55 is a perspective view showing a waveguide path type CO₂ laserapparatus according to an Embodiment 41 of the present invention;

FIG. 56 is a perspective view showing essential parts of a waveguidepath type CO₂ laser apparatus according to an Embodiment 42 of thepresent invention;

FIG. 57 is a perspective view of a solid laser apparatus according to anEmbodiment 43 of the present invention;

FIG. 58 is a perspective view showing essential parts of a solid laserapparatus according to an Embodiment 44 of the present invention;

FIG. 59 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 45 of the presentinvention;

FIG. 60 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 46 of the presentinvention;

FIG. 61 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 47 of the presentinvention;

FIG. 62 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 50 of the presentinvention;

FIG. 63 is a view showing the characteristics under the condition thatthe spacing between electrodes of the laser apparatus shown in FIG. 62is 5 mm;

FIG. 64 is a view showing the characteristics under the condition thatthe spacing between electrodes of the laser apparatus shown in FIG. 62is 15 mm;

FIG. 65 is a sectional view showing a waveguide path type CO₂ laserapparatus according to an Embodiment 51 of the present invention;

FIG. 66 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 52 of the presentinvention;

FIG. 67 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 53 of the presentinvention;

FIG. 68 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to an Embodiment 54 of the presentinvention;

FIG. 69 is a perspective view showing a conventional waveguide path typeCO₂ laser apparatus;

FIG. 70 is a graphic representation showing the relationship between thedischarge space and the coefficient of laser excitation in the CO₂ laserapparatus shown in FIG. 69;

FIG. 71 is a graphic representation showing the gap length and thecooling capacity in the CO₂ laser apparatus shown in FIG. 69;

FIG. 72 is a graphic representation showing the relationship between thefrequency of the excitation power source and the efficiency of the laserexcitation in the laser apparatus shown in FIG. 69;

FIG. 73 is a graphic representation showing the relationship between thefrequency of the excitation power source and the electric-fielddistribution in the laser apparatus shown in FIG. 69;

FIG. 74 is an explanatory view of the discharge toward a resonatormirror in the laser apparatus shown in FIG. 69;

FIG. 75 is a view showing the oscillation characteristics at the time ofoccurrence of the discharge toward the resonator mirror in the laserapparatus shown in FIG. 69; and

FIG. 76 is an explanatory view of the discharge occurring in the end ofa dielectric in the laser apparatus shown in FIG. 69.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to FIGS. 1 to 32. In those figures, like elements(members) to those described hereinabove with reference to FIGS. 33 to39 are denoted by like reference numerals and characters, and detaileddescription thereof is omitted herein.

EMBODIMENT 1

FIG. 1 is a schematic sectional view showing a gas laser apparatusaccording to the Embodiment 1 of the present invention. The present gaslaser apparatus has a rectangular section wherein the ratio between thelengths of the major side and the minor side is equal to or higher than3, and is extracted a laser beam in the direction perpendicular to thesection. Also in the present embodiment, cooling water flows through theelectrodes 1 and 2 in order to cool the laser medium.

While the basic construction of the present gas laser apparatus issimilar to the conventional gas laser apparatus shown in FIG. 69, in thepresent embodiment, the dielectric plates 10 and 20 are provided with athickness distribution in order to provide the electrostatic capacitiesof the electrodes with a distribution to generate the discharge inoblique directions in the section.

Subsequently, operation of the present gas laser apparatus will bedescribed. When an ac high voltage is applied between the metalelectrodes 1 and 2, the discharge is generated in the discharge space 4.In this instance, since discharge energy is poured in in proportion tothe electrostatic capacity, if a suitable distribution is provided tothe thicknesses of the dielectric plates 10 and 20, then such dischargein oblique directions as indicated by reference character DC in FIG. 1is caused. According to an experiment of the inventors, it was confirmedthat, when a thickness distribution is to be provided to a samedielectric material, the discharge in oblique directions is causedprincipally if the ratio in thickness between a thinner portion and athicker portion is set to 1:3 or more.

According to this embodiment, since an equivalent discharge gap lengthin oblique direction can be set arbitrarily by selecting the pitch(reference p) at thinner portions of the dielectric plates 10 and 20,optimization can be achieved by the power source frequency.

FIGS. 2 and 3 illustrate results of an examination of the power sourcefrequency dependency of the laser output at p=5 mm and 15 mm,respectively, in the condition of the gap length of 2 mm. Under thecondition of p=5 mm of FIG. 2, the excitation efficiencies at the powersource frequencies of 150 MHz and 13.56 MHz are substantially equal toeach other. Further, under the condition of p=15 mm of FIG. 3, also theexcitation efficiency at 100 kHz is almost equal, and enhancement inlaser excitation efficiency in a low frequency region is confirmed.Accordingly, it can be recognized that, if the equivalent discharge gaplength is taken long by the oblique discharge provided by the presentembodiment, even where a power source of a lower frequency is used,laser oscillation of a high efficiency is possible.

EMBODIMENT 2

It was confirmed that, if the metal electrodes 1 and 2 are molded withdielectric members 101 and 201 having a low dielectric constant as shownin FIG. 4, then it is possible to apply a higher voltage between themand an increase in output power is realized.

EMBODIMENT 3

Meanwhile, even if different dielectrics 102 and 202 are laminated onthe dielectric plates 10 and 20, respectively, to form steppeddielectric layers as shown in FIG. 5, similar effects to those of theEmbodiment 1 can be obtained. In this instance, if the dielectrics 102and 202 are formed from a material having a lower dielectric constantthan that of the dielectric plates 10 and 20, then it is possible toreduce the thicknesses of the dielectrics 102 and 202 to raise theeffect of heat conduction for cooling the mixture gas.

EMBODIMENT 4

Meanwhile, if the neutral point of the power source is grounded so thatvoltages having the opposite polarities to each other (voltagesdisplaced by 180° from each other in phase) are applied to the metalelectrodes 1 and 2, then the insulation distances from the electrodes 1and 2 to the ground can be designed short, and a compact laseroscillator can be realized.

EMBODIMENT 5

While the effects of the oblique discharge in the section of thedischarge space 4 perpendicular to the optic axis are described in theEmbodiment 1, similar effects to those of the Embodiment 1 can beobtained even if oblique discharge occurs in the direction of the opticaxis as shown in FIG. 7.

EMBODIMENT 6

While the cases wherein the discharge is caused in oblique directions bya distribution of the electrostatic capacity are described in theembodiments described above, if, for example, as shown in FIG. 8, themetal electrodes 1 and 2 which are opposed to each other and anotherpair of metal electrodes 11 and 22 which are opposed to each other areshort-circuited by way of the dielectric members 10 and 20 while a highvoltage is applied between the adjacent metal electrodes 1 and 11 andthe adjacent metal electrodes 2 and 22, then the discharge is causedbetween obliquely opposed electrodes having different potentials (inshort, between the electrodes 1 and 22 and between the electrodes 2 and11) and between adjacent electrodes (in short, between the electrodes 1and 11 and between the electrodes 2 and 22). Consequently, similareffects to those described above are obtained. In short, if thedischarge can be caused in oblique directions with respect to thedielectric members 10 and 20, then laser excitation of a high efficiencyis possible even when a power source of a low frequency is employed.

EMBODIMENT 7

FIG. 9 is a schematic view showing a gas laser apparatus according tothe Embodiment 7 of the present invention. The basic construction of thepresent gas laser apparatus is similar to that shown in FIG. 69.However, in the present embodiment, the discharge electrodes 1 and 2 aredisposed in the direction of the major side of the section of thedischarge space 4 as shown in FIG. 9, and the discharge is caused in thedirection of the major side of the discharge space 4.

Since the ratio between the major side and the minor side (i.e., theaspect ratio) of the discharge space 4 is set equal to or higher than 3similarly as in the Embodiment 1, the gap length can be increased bythree or more times only by changing the direction of the discharge fromthe direction of the minor side to the direction of the major side.Consequently, the gap travel time t_(e) of electrons describedhereinabove is increased, and the electric field strength is put into acondition optimum for laser oscillation and laser oscillation of a highefficiency is realized even where the RF power source 3 has a lowfrequency with a comparatively long power source period t_(s).

A result of a similar oscillation experiment which was conducted undersimilar conditions to those of FIG. 72 using the gas laser apparatus ofthe present embodiment is shown in FIG. 10. It can be seen from FIG. 10that the laser oscillation efficiency in a low frequency region isimproved. If the aspect ratio is further increased, then the laseroscillation efficiency will rely upon the power source frequency littlemore.

EMBODIMENT 8

In the present embodiment, the construction of the Embodiment 7described above is modified such that, as shown in FIG. 11, dischargeelectrodes 111 and 221 are surrounded by dielectric members 103 and 203of glass or the like, respectively. Also with this construction, similareffects to those of the Embodiment 7 can be exhibited (common with theEmbodiment 1 in that a pair of dielectric members are disposed betweenthe discharge electrodes).

EMBODIMENT 9

In the present embodiment, the construction of the Embodiment 7described above is modified such that, as shown in FIG. 12, a dc powersource 31 is employed to excite the laser by the dc glow discharge. Thedc power source 31 is connected to a cathode pin electrode 112 and ananode 222. Also with the present construction, similar effects to thoseof the Embodiment 7 can be exhibited.

EMBODIMENT 10

The present embodiment has such construction which is a combination ofthe constructions of the Embodiments 7 and 9, and as shown in FIG. 13,in the present embodiment, the discharge for supplying energy lower thanone half the power in the direction of the major side by the dc powersource 31 is caused in the direction of the minor side by the RF powersource 3. By this construction, the discharge in the direction of themajor side is facilitated (so as to allow the discharge to be causedwithout applying an over-voltage). Further, the discharge can bestabilized.

It is to be noted that, while a CO₂ laser is taken as an example in theembodiments described above, the present invention can be applied tosuch other gas lasers as a CO laser which are required to assureexcitation by low energy electrons similarly to a CO₂ laser.

EMBODIMENT 11

FIG. 14 is a sectional view showing a gas laser apparatus according tothe Embodiment 11 of the present invention. Referring to FIG. 14,reference numerals 1 and 2 each denote a metal electrode, and 13 and 23each denote a metal angular pipe (through which cooling watercirculates). A plurality of metal electrodes 1 and 2 are connected tothe dielectric members 10 and 20, respectively, and are connected to theac power source 3. The metal electrodes 1 and 2 are disposed in analternate relationship on the opposite sides of the discharge space 4.

Further, a metal pipe 13 or 23 in the electrically floating condition isdisposed between each adjacent ones of metal electrodes 1 or 2. Themetal electrodes 1, 2 and the metal angular pipes 13, 23 are cooledindividually, and the laser gas in the discharge space 4 is cooled byway of the dielectric plates 10 and 20. Further, dielectric materials 15and 25 are molded to cover over the entire electrodes 1, 2 and metalangular pipes 13, 23 to prevent the creeping discharge.

Subsequently, operation will be described. If an ac high voltage isapplied from the RF power source 3 between the metal electrodes 1 and 2,then the predischarge 44 is caused in the direction of the minor side ofthe discharge space 4. Then, if the voltage is further raised, the maindischarge 45 is caused in oblique directions.

This phenomenon will be described by way of an equivalent circuit of anelectrode system shown in FIG. 15. The main discharge (plasma resistanceR₁) 45 is, on one hand, connected to the power source 3 by way of anelectrostatic capacity C₁ of the dielectric plate 10 (from the feedelectrode 1) and, on the other hand, connected to the power source 3 byway of an electrostatic capacity C₁ of the other dielectric plate 20(from the feed electrode 2).

Meanwhile, the preliminary discharge (plasma resistance R₂) 44 isconnected, when it is connected to the feed electrode 1 by way of themetal angular pipe 13, to the feed electrode 1 by way the electrostaticcapacity C₁ of the dielectric plate 10, the metal angular pipe 13 and anelectrostatic capacity C₂ of the dielectric material 15. On the otherhand, when the preliminary discharge 44 is connected to the metalangular pipe 23 by way of the feed electrode 2, it is connected to thefeed electrode 2 by way of the electrostatic capacity C₁ of thedielectric plate 20. Due to these connection configurations, thepreliminary discharge 44 is caused between the metal angular pipe 13 andthe feed electrode 2 and similarly between the feed electrode 1 and themetal angular pipe 13.

In the present embodiment, the preliminary discharge starts at a verylow voltage because the equivalent gap length in the direction of theminor side is short. Then, the discharge field is put into a weaklyionized condition by ultraviolet rays or charged particles generated bythe preliminary discharge 44, and the main discharge 45 is fired at acomparatively low voltage.

A difference in thrown-in power characteristics arising from whether thepreliminary discharge is present or absent is shown in FIG. 16.Referring to FIG. 16, a solid line EX. II shows a thrown-in powercharacteristic when the preliminary discharge 44 is present, and abroken line shows another thrown-in power characteristic when thepreliminary discharge 44 is absent. When there is no preliminarydischarge, the main discharge 45 is not fired until after a high voltage(over-voltage) is applied once, and high energy is poured into thedischarge field suddenly. However, when a preliminary ionizing mechanismis added to cause the preliminary discharge 44 as in the presentembodiment, the main discharge 45 is fired smoothly, and anuncontrollable region (region until discharge is reached) which appearsin conventional apparatus can be eliminated.

By the way, since the preliminary discharge 44 is the discharge whereinthe equivalent gap length is small, there is a drawback that, if thehigh power is thrown-in for the preliminary discharge 44 is increased,then as described hereinabove in connection with the prior art, thelaser excitation efficiency decreases at a low power source frequencybelow 100 MHz. The inventors confirmed that, if the power to be thrownin for the preliminary discharge 44 is set to a value equal to or lowerthan 10% of the power to be thrown in for the main discharge 45, thenthe role of the preliminary discharge can be exhibited sufficientlywithout deteriorating the excitation efficiency of the laser by (thepreliminary discharge)+(main discharge).

In this instance, as seen from FIG. 15, in both of the preliminarydischarge 44 and the main discharge 45, the discharge energy (power) ispoured in proportion to the electrostatic capacities C₁ and C₁ +C₂,respectively, of the dielectric members corresponding to the discharge.Accordingly, the power to be thrown in for the preliminary discharge 44can be set equal to or lower than 10% of the electric power to be thrownin for the main discharge 45 by setting the electrostatic capacity ofthe dielectric members corresponding to the preliminary discharge 44 toa value equal to or lower than 10% of the electrostatic capacity for themain discharge 45.

EMBODIMENT 12

While, in the Embodiment 11 described above, the main discharge (obliquedischarge) 45 and the preliminary discharge 44 are described as beingcaused in the plane perpendicular to the optic axis of the rectangulardischarge space 4, similar effects to those of the Embodiment 11 can beobtained even if the main discharge 45 and the preliminary discharge 44are caused in the direction of the optic axis as in the presentEmbodiment 12 shown in FIG. 17. However, in FIG. 17, only the maindischarge 45 is shown while the preliminary discharge 44 is omitted.Also the dielectric molded elements are omitted.

EMBODIMENT 13

Further, while, in the Embodiments 11 and 12, power is fed for thepreliminary discharge 44 and the main discharge 45 from the common powersource 3, similar effects to those of the Embodiments 11 and 12 can beobtained even if energy is supplied separately for the preliminarydischarge 44 and the main discharge 45 from separate power sources 3 and32 as in the Embodiment 13 shown in FIG. 18.

EMBODIMENT 14

FIG. 19 is a perspective view showing a gas laser apparatus according tothe Embodiment 14 of the present invention. The gas laser apparatus ofthe present embodiment is different from the conventional gas laserapparatus shown in FIG. 69 in that the lengthwise dimension and thewidthwise dimension of the metal electrodes 1 and 2 are set shorter thanthe lengthwise dimension and the widthwise dimension, respectively, ofthe dielectric plates 10 and 20 by 5 mm or more.

In the present embodiment, since the lengthwise dimension and thewidthwise dimension of the metal electrodes 1 and 2 are smaller than thelengthwise dimension and the widthwise dimension, respectively, of thedielectric plates 10 and 20 by 5 mm or more, also when the dischargepower is increased (when the applied voltage is raised), concentrationof the discharge 42 by concentration of the electric field at the cornerportions of the dielectric plates 10 and 20 (refer to FIG. 76) can beprevented.

Meanwhile, also the occurrence of the discharge 41 toward the outputcoupler 8 shown in FIG. 74 depends much upon the applied voltage. In thefollowing, the discharge 41 will be described. In the Embodiment 14,where the gap length is represented by d, the distance between thedielectric plates 10, 20 and the output coupler 8 by L_(wm), thedifference in length between the metal electrodes 1, 2 and thedielectric plates 10, 20 by L, the discharge starting voltage by V* andthe applied voltage peak value by Vo_(p), the design standard of thedistance (L_(wm) +L) between the output coupler 8 and the metalelectrodes 1, 2 is set in accordance with the following equation (3):

    L+L.sub.wm ≧(Vo.sub.p /V*)d                         (3)

(Vo_(p) is an adjustable variable, and V* and d are fixed values.)

It was proved experimentally by the inventors that, under the conditionswherein the equation (3) is satisfied, no discharge 41 toward the outputcoupler 8 is caused. Further, the discharge power W_(d) is obtained fromthe power source frequency f and the dielectric electrostatic capacity Cof the discharging section in accordance with the following equation(4):

    W.sub.d =πfCV*(Vo.sub.p.sup.2 -V*.sup.2).sup.1/2        (4)

(C and f are fixed values.)

Accordingly, as apparent from the equations (3) and (4), when a highdischarge power W_(d) is to be PG,50 thrown in, Vo_(p), that is, (L_(wm)+L), should be set to a high value.

Consequently, if the distance (L_(wm) +L) between the output coupler 8and the metal electrodes 1, 2 is set to a large value, then even if theapplied voltage is raised, occurrence of the discharge toward theoptical resonator mirror 7 can be prevented.

EMBODIMENT 15

Further, if the construction of the Embodiment 14 described above ismodified such that the width W of the metal electrodes 1 and 2 is setsubstantially equal to the width of a laser beam passing between themwhich is determined by the optical resonator as in the presentembodiment shown in FIGS. 20A and 20B, then the discharge energy can beconverted into light energy without a loss.

EMBODIMENT 16

In the present embodiment, making use of the fact that the width of themetal electrodes 1 and 2 is smaller than the width W' of the dielectricplates 10 and 20, a pair of spacers 16 and 17 are disposed between thedielectric plates 10 and 20 between which the metal electrodes 1 and 2are not present as shown in FIGS. 21A and 21B so that the distancebetween the surfaces (light reflecting faces) of the dielectric plates10 and 20 is kept fixed.

Consequently, the gap distance between the dielectric plates 10 and 20can be kept fixed without having an influence on the discharge of alaser beam. It is to be noted that, if the spacers 16 and 17 areconstituted from an incombustible material against a laser beam, then alaser beam which may be produced other than in the direction of theregular optic axis by diffracted light of a laser beam or mis-alignmentof the resonator causes no undesirable effect.

Further, since the spacers 16 and 17 are formed from an insulatingsubstance such as ceramics, they do not have an influence on thedischarge at all and the anticipated objects can be achieved.

Furthermore, if the spacers 16 and 17 are constituted from a metal, theycan be produced at a low cost. In this instance, the somewhat pincheddischarge is observed at the spacer portions. However, according to theinventors, it was confirmed that the discharge does not have aninfluence on the laser characteristic.

EMBODIMENT 17

FIG. 22 is a sectional view showing the Embodiment 17 of the presentinvention. Referring to FIG. 22, reference characters 1a and 2a eachdenote a conducting member, and 10a, 10b, 20a and 20b each denote adielectric plate. The dielectric plates 10a, 10b, 20a and 20b may eachbe made of a metal plate which is coated with a dielectric layer. Withthis construction, the heat transfer rates of the dielectric plates 10a,10b, 20a and 20b are raised, and the gas cooling efficiency is enhanced.

The dielectric plate 10a is disposed in an opposing relationship to thedielectric plate 10, and the dielectric plate 20a is disposed in anopposing relationship to the dielectric plate 20. Further, thedielectric plates 10b and 20b are disposed in an opposing relationshipto each other. And, the conductive bodies 1a and 2a are held between thedielectric plates 10a and 10b and between the dielectric plates 20a and20b, respectively, so that they are in an electrically floatingcondition.

Accordingly, the discharge space 4 is divided into three dischargespaces 4a, 4b and 4c. Further, the conductive bodies 1a and 2a and thefeed electrodes 1, 2 are kept in a condition in which they are cooledwith water.

Subsequently, operation will be described. With the gas laser apparatusof the present embodiment, since the discharge space 4 is divided intothe three discharge spaces 4a, 4b and 4c and the feed electrodes 1 and 2and the conductive bodies 1a, 2a are cooled with water, laser gasproduced in the discharge spaces 4a, 4b and 4c is cooled efficiently.

Meanwhile, since a high electric field portion for maintaining thedischarge appears in the proximity of each of the feed electrodes 1 and2, the discharge space 4b which is spaced away from the high electricfield portions becomes a region of a low electric field which issuitable for laser oscillation. Accordingly, even when a low frequencypower source is employed, if attention is paid to the discharge space4b, then it is superior in cooling capacity and excitation of a highefficiency is possible.

Further, since the efficiency of a lower frequency power source ishigher than the efficiency of a high frequency power source, the laseroutput which is extracted per unit length of the discharge is as high asthat excited by a high frequency. In particular, while the dischargeenergy thrown into the spaces 4a and 4c makes a loss, since theefficiency of a low frequency power source is higher than the efficiencyof a high frequency power source, it is possible to design theefficiency of the entire gas laser apparatus so that it may be equal tothe excitation efficiency of a high frequency.

Furthermore, if the light path of a laser beam is turned back so as toutilize the energy of the discharge spaces 4a and 4c again, then theefficiency of the gas laser apparatus can be further enhanced.

EMBODIMENT 18

While, in the preceding Embodiment 17, the dielectric plates 10a and 10bare provided at the opposite end portions of the conductive body 1awhile the dielectric plates 20a and 20b are provided at the opposite endportions of the conductive body 2a and the discharge space 4 is dividedinto the three discharge spaces 4a, 4b and 4c, similar effects can beobtained even by disposing a pair of dielectric plates 10c and 20c in apredetermined spaced relationship between the discharge spaces 4a, 4band 4c as in the present embodiment shown in FIG. 23. However, in thisinstance, it is necessary to cool the dielectric plates 10c and 20c, andaccordingly, it is necessary to select a material having a high heattransfer rate.

EMBODIMENT 19

Further, while, in the preceding Embodiment 17, the feed electrodes 1and 2 are coated with dielectric layers, metal electrodes 19 and 29which are not coated with dielectric layers as shown in FIG. 24 mayalternatively be employed. In this instance, the ends of the metalelectrodes 19 and 29 should be made sharp or pointed so as to settle theoccurring positions of the discharge 4d and 4f from the metal electrodes19 and 29. It is to be noted that reference character 4e denotes adischarge space.

While a CO₂ laser is described by way of an example in the Embodiments17 to 19, the present invention can be applied to other gas lasers suchas a CO laser which are required to cause excitation by low energyelectrons similarly to a CO₂ laser.

EMBODIMENT 20

FIG. 25 is a perspective view showing the Embodiment 20 of the presentinvention. Referring to FIG. 25, reference numeral 105 denotes an outerpipe formed in a cylindrical profile, and 205 an inner pipe formed in acylindrical profile. The outer and inner pipes 105 and 205 are eachformed from a dielectric plate and are disposed on a common axis. Adischarge space 4 is formed between the outer and inner pipes 105 and205 and has a cylindrical profile (having a doughnut-shaped section).

The feed electrodes 1 and 2 are disposed on an outer periphery of theouter pipe 105 and connected to the ac power source 3. The inner pipe205 is formed from a conductor and is normally cooled in an electricallyfloating condition. Further, the distance (discharge gap: d) between theinner and outer pipes 205 and 105 is set to 2 mm.

In the present embodiment, if a high ac voltage is applied between theelectrodes 1 and 2, then the discharge is caused in the discharge space4. Gas present in the discharge space 4 is excited by the discharge sothat a laser beam 9 is extracted to the outside from the opticalresonator mirrors 7 and 8 disposed in the proximity of the opposite endsof the discharge space 4. In this instance, the outer surface of theinner pipe 205 and the inner surface of the outer pipe 105 act as waveguides for the laser beam.

When the applied voltage is low, the discharge is caused only in theproximity of the feed electrodes 1 and 2 as shown in FIG. 26A. However,if compared with the flat plate electrodes shown in FIG. 19 and soforth, the equivalent gap length is twice, and accordingly, excitationwith high efficiency is possible. Meanwhile, if the applied voltagerises, then the discharge spreads to the entire discharge space 4 asseen in FIG. 26B, and consequently, good laser excitation having a longequivalent gap length is possible.

EMBODIMENT 21

Meanwhile, if the construction of the preceding Embodiment 20 ismodified such that a plurality of feed electrodes 1b and 2b are providedin addition to the feed electrodes 1 and 2 as shown in FIG. 27, there isan effect that, even if the voltage to be applied to each electrode islow, the discharge spreads to the entire region.

EMBODIMENT 22

While the preceding Embodiments 20 and 21 show an example which employsa common power source, separate power sources may otherwise be connectedto the different electrodes. Further, similar effects can be obtainedeven where a polyphase power source 33 is employed as shown in FIG. 28(in which the power source 33 shown is a three-phase power source).

It is to be noted that, if the inner pipe 205 shown in FIGS. 25 to 28 isconstituted from a dielectric, then concentration of the discharge inthe proximity of the feed electrodes is moderated and the furtherdiffusive discharge can be realized.

EMBODIMENT 23

Further, if a composite pipe wherein a metal pipe 121 is attached on aninner peripheral face of a dielectric layer 122 of glass or the like isused as the inner tube and cooling water flows in the metal pipe 121 inplace of the dielectric layer 122 as shown in FIG. 29, then even if thedielectric layer 122 is damaged by discharge energy, there is nopossibility of leakage of water.

Further, in FIG. 29, since the metal pipe 121 is grounded using aneutral point grounding power source 34, the discharge spreads in theentire discharge space 4 at a further low voltage.

EMBODIMENT 24

Further, the construction of the Embodiment 20 is modified such that apair of metal elements 123 and 124 which are in an electrically floatingcondition and have a self cooling function are disposed in an alternaterelationship with the feed electrodes 1 and 2 at locations on the outerperiphery of the outer pipe 105 where the feed electrodes 1 and 2 arenot provided as shown in FIG. 30. Laser gas in the discharge space 4 canbe cooled further effectively.

EMBODIMENT 25

While the case wherein the discharge is caused in radial directions ofthe cylindrical discharge space 4 is described in the Embodiments 20 to24, the present invention is not limited to this, and quite similareffects to those of the embodiments can be obtained even if a pluralityof electrodes 106 and 107 which are divided in the outgoing direction ofa laser beam are provided as shown in FIG. 31.

In particular, where the discharge is caused in the direction of theoptic axis, the gap length g can be set arbitrarily. Accordingly, laserexcitation of a high efficiency can be performed even if a power sourceof a low frequency is used. In this instance, the uniformity of thedischarge on the annular sectional area of the discharge space 4 is verysuperior.

Further, while the single RF power source 3 is employed in the presentembodiment, otherwise a plurality of power sources or such a polyphasepower source 33 as shown in FIG. 28 may be employed instead.

EMBODIMENT 26

The inner tube 205 may be formed from a metal, a dielectric or a metalhaving a dielectric coated on the surface thereof as describedhereinabove in connection with the Embodiments 20 to 25. Particularlywhere the neutral point grounding power source 34 is used as shown inFIG. 32 and the inner pipe is grounded, when the discharge startsbetween the metal inner pipe 205 and the feed electrodes 106, 107, 108and 109, the discharge region is expanded as the applied voltage rises,and accordingly, the construction is practical without the necessity ofan over-voltage. Particularly where the metal inner pipe 121 is coatedwith the dielectric 122, discharge is further uniformed and the effectis high.

Furthermore, while a CO₂ laser is described in the Embodiments 20 to 26,the present invention is not limited to this and can be applied to someother gas lasers such as a CO laser which is required to assureexcitation by low energy electrons.

EMBODIMENT 27

FIG. 33 is a perspective view of a laser apparatus according toEmbodiment 27 of the present invention. In this figure, referencenumeral 70 designates a laser beam output window as the atmosphereshield window arranged on the side of the output coupler 8 for removinga laser beam. This output window 70 is installed away from the outputcoupler 8.

Accordingly, a portion between the output coupler 8 and the outputwindow 70 forms a non-discharge portion (a non-excitation portion)through which a laser beam 9 passes. In this non-discharge portion isarranged a cooling duct 711 as a laser gas cooling means.

The cooling duct 711 has a rectangular opening in the central portionthereof. The length of major side and minor side of the rectangularopening is set to three times or less of the major side and the minorside of the laser beam which passes through the cooling duct 711.

Further, in the Embodiment 27, dimensions of the lengths of metalelectrodes 1 and 2 are set to be shorter than dimensions of the lengthof dielectric plates 10 and 20. Both lengthwise ends of the dielectricplates 10 and 20 are extended toward the reflection mirrors 7 and 8 fromboth lengthwise ends of the metal electrodes 1 and 2.

Accordingly, a portion between the metal electrodes 1, 2 and thereflection mirrors 7, 8 also forms a non-discharge portion (anon-excitation portion). In these non-discharge portions are arranged,as laser gas cooling means, cooling pipes 712, 713 and 714, 715 having acooling function which are electrically floated or grounded.

Generally, since the output coupler 8 and the output window 70 arearranged away from each other, the laser beam can be naturallypropagated to increase a beam diameter at the position of the outputwindow 70.

In FIG. 33, the output coupler 8 and the output window 70 are merelyarranged away from each other, FIG. 35 shows the characteristics oflaser oscillation of a conventional laser apparatus having no laser gascooling means.

As will be apparent from FIG. 35, a laser output along with a dischargeelectric power linearly extends in a low output region. However, asaturation phenomenon of output is once observed at a position wherelaser output is approximately 500 W, and it has been confirmed that asan input increases, a laser output again increases. It has been foundthat an inclination (efficiency) of the laser output after saturation islower than that prior to saturation. It has become clear that theintensity of light at which output is saturated largely depends upon theconcentration of carbon dioxide, and the lower the concentration ofcarbon dioxide, the output saturation is harder to occur.

It has been found as the result of the detailed study that the aforesaidphenomenon is the saturation phenomenon of the output due to theabsorption of the laser light of carbon dioxide gas in thenon-excitation and non-cooling space. That is, the saturation phenomenonof the output results from the effect of light absorption in the spacewhich is not excited (in which reversal distribution is not formed) andwhich is not cooled, for example, in the space between the dischargespace 4 and the reflection mirrors 7, 8 or between the output coupler 8and the output window 70.

Now, the relationship between the coefficient of light absorption of thecarbon dioxide gas and the gas temperature is shown in FIG. 36. As willbe apparent from FIG. 36, it is understood that as the gas temperaturerises, the coefficient of light absorption increases, and finally asaturation occurs. That is, the process is repeated such that in thenon-excitation space, the carbon dioxide gas absorbs the energy of thelaser beam to induce a rise of gas temperature and the absorption amountof the energy increases. In this process, even if the input increases,the absorption amount of light increases, and therefore the laser outputdoes not increase, and when the gas temperature reaches approximately600 K., the coefficient of light absorption stops increasing.

As described above, the conventional laser apparatus has problems inthat the effect of light absorption increases in the non-excitationspace and non-cooling space particularly at the time of high laseroutput increases, and by this effect of light absorption, the saturationphenomenon of laser output occurs or the oscillation efficiency lowers.

However, in this Embodiment 27, the laser gas cooling means (the coolingduct 711 and the cooling pipes 712, 713, 714 and 715) is provided in thenon-discharge portions in the passage of the laser beam (between theoutput coupler 8 and the output window 70, and between the metalelectrodes 1, 2 and the reflection mirrors 7, 8), whereby in thenon-discharge portion (non-excitation space) where no reversaldistribution occurs, heat caused by light absorption is present but thecooling thereof is sufficiently carried out so that the effect of lightabsorption can be minimized. Thereby, the rise of gas temperature issmall. Accordingly, the coefficient of light absorption is suppressed toa low value, and the laser output with a high efficiency becomespossible.

FIG. 34 is a view showing the characteristics of laser oscillationaccording to Embodiment 27. As will be apparent from this figure,according to Embodiment 27, the saturation phenomenon of the laseroutput and the lowering of the oscillation efficiency as seen in FIG. 35are not at all observed, and the laser apparatus with high efficiency isobtained.

FIG. 37 is a perspective view of a laser apparatus according toEmbodiment 28 of the present invention. In the Embodiment 28, a smallblower or the like is installed as a gas flow generating means so thatas indicated by the arrow in the non-excitation portion, gas flows 150,160 are forcibly generated, and the temperature rise of the laser gas atthe non-excitation portion is suppressed by the gas flows 150, 160. Thisalso provides the effect similar to that of the Embodiment 27.

EMBODIMENT 29

FIG. 38 is a perspective view of a laser apparatus according toEmbodiment 29 of the present invention. In this Embodiment 29, sideplates 51 and 52 for preventing a leakage of laser gas are provided onboth sides of a discharge space 4 formed between dielectric plates 10and 20. Gas flow passages 51a and 52a (only 51a is shown) are providedin the midst of the side plates 51 and 52. A laser gas is supplied fromthe gas flow passages 51a and 52a into the discharge space 4 asindicated by arrows 170 and 180, and gas is always exhausted by a vacuumpump (not shown) so that gas pressure in the discharge space 4 isconstant.

With the construction as described above, a gas flow occurs from thecentral portion of the discharge space 4 toward the reflection mirrors 7and 8, and the similar effect is obtained. In this case, in thedischarge space 4, the carbon dioxide gas is subjected to electroncollision and dissociated into carbon monoxide and oxygen as given bythe following formula:

    CO.sub.2 +e→CO+O.sub.2 /2

For this reason, there is a most generous effect of obtaining an idealsituation wherein in the discharge space, the concentration of carbondioxide gas is high, and in the non-excitation space, the concentrationof carbon dioxide gas is low. From a view point that a low temperaturegas flows into the non-excitation portion, the flow of the laser gas(arrows 170, 180) in FIG. 38 may be reversed. That is, it is significantto provide an arrangement wherein a laser gas is introduced from thenon-excitation portion into the discharge space 4 and a laser gas isdischarged from the central portion of the electrode (gas flow passages51a, 52a of the side plates 51, 52).

While in the Embodiment 29, the case has been described in which thedissociation phenomenon of the carbon dioxide caused by discharge isutilized to provide a difference in the concentration of carbon dioxidebetween the excitation space and the non-excitation space, it is to benoted in short that if the concentration of carbon dioxide in thenon-excitation space is suppressed to be low, a similar effect isobtained.

EMBODIMENT 30

FIG. 39 is a perspective view of a waveguide path type CO₂ laserapparatus according to Embodiment 30 of the present invention. In thisEmbodiment 30, a pair of flat-plate like metal electrodes 1, 2 opposedto each other and dielectric plates 10, 20 plated in close contact withthe opposed surfaces of the metal electrodes 1, 2 to form a dischargespace 4 having a rectangular section therebetween constitute one unit,and such four units U1, U2, U3 and U4 are arranged to have a polygonalshape in section (a square shape in section).

With such a construction as described, each of four discharge spaces 4ato 4d formed in the four units U1 to U4 is in the state arranged in apolygonal shape (a square shape in section).

In the Embodiment 30, the one metal electrode 1 of each of the units U1to U4 is connected to an excitation power source (RF power source) 3,and the discharge spaces 4a to 4d are filled with a mixture gassimilarly to prior art.

Further, in the Embodiment 30, reflection mirrors 7, 8 arrangedopposedly on both lengthwise end openings of the discharge spaces 4a to4d are comprised of a series of folded mirror plate portions 71, 72 and81, 82 folded at a suitable angle through folded lines 7a, 8a, theirfolding directions being arranged to be different by 90°.

More detailedly, in FIG. 40 which shows a beam light path of a laserbeam of the waveguide path type CO₂ laser apparatus shown in FIG. 39, L1and L2 represent two linear symmetrical axes which pass a center pointof a space section which is surrounded by the discharge spaces 4a, 4b,4c and 4d to form a beam light path. The reflection mirrors 7 and 8 arearranged so that one out of the linear symmetrical axes L1 and L2accords with the folding lines 7a, 8a of the reflection mirrors 7, 8,and the directions of the folding lines 7a, 8a are different by 90°.

The linear symmetrical lines L1 and L2 termed herein mean that the spacesection is symmetrical to left and right with respect to a certain line.For example, in FIG. 40, in the case where the dotted lines are arrangedin section of the discharge spaces 4a, 4b, 4c and 4d, when the dischargespace section is folded at the portion of the linear symmetric axis L1or L2, the folded discharge space sections are exactly overlapped toprovide an accorded line.

In the reflection mirrors 7 and 8 folded as described above, arectangular laser beam emitting port 83 as shown in FIG. 39 is providedon the reflection mirror 8 on the laser beam removing side.

In FIG. 40, reference numeral 9a designates a laser beam which ispresent in the discharge spaces 4a, 4b, 4c and 4d. In FIG. 39, referencenumeral 39 designates a laser beam which is emitted from the laser beamemitting port 83.

The operation will be described hereinbelow.

In FIG. 40, the laser beam 9a is reflected downwardly in the directionof the arrow from a black point P of an upper folded mirror plateportion 81 in output coupler 8 and moves forward. The laser beam 9a isturned back and reflected in the direction of one folded mirror plateportion 71 of the other reflection mirror 7 at a lower folded mirrorplate portion 82. Then, the laser beam is turned back and reflected inthe lateral direction from the folded mirror plate portion 71 toward theother folded mirror plate portion 72 continuous thereto, and thereafterthe laser beam is turned back and reflected toward the lower foldedmirror plate portion 82 of the one reflection mirror 8 at the foldedmirror plate portion 72. In the lower folded mirror plate portion 82,the light beam is turned back and reflected toward the upper foldedmirror plate portion 81. In the lower folded mirror plate portion 81,the laser beam is turned back and reflected in the direction of the onefolded mirror plate portion 72 (left side in the figure) of the otherreflection mirror 7. In this folded mirror plate portion 72, the laserbeam is turned back and reflected in the direction of the other foldedmirror plate portion 71 (right side in the figure) and thereafter turnedback and reflected so as to be returned to the black point P from thefolded mirror plate portion 71.

That is, in the output coupler 8, the incident laser beam 9a from theother reflection mirror 7 is turned back and reflected vertically, andin the other reflection mirror 7, the incident laser beam 9a from theoutput coupler 8 is turned back and reflected in the lateral direction.

Accordingly, the light path of the laser beam 9a which is turned back atthe one reflection mirror 7 and is again reflected in the direction ofthe output coupler 8 is not reversely returned along one and the samelight path unlike the light path of the laser beam before being turnedback and reflected as previously mentioned.

The laser beam 9a returned to the one reflection mirror 8 is at aposition separately from the black point P (the folded mirror plateportion 81 having the black point P is the folded mirror plate portion82), and the laser beam 9a is again turned back upwardly (the foldedmirror plate portion 81) from that position, and turned back andreflected in the direction of the folded mirror plate portion 72 of theother reflection mirror 7. The laser beam 9a reaching the folded mirrorplate portion 72 is turned back and reflected in the direction of thefolded mirror plate portion 71, and then the laser beam is folded backand reflected in the direction of the folded mirror plate portion 81 ofthe other reflection mirror at the folded mirror plate portion 71, andreturned to the black point P.

As described above, the laser beam 9a is continuous as a single beam,and four beam paths which reciprocate between the reflection mirrors 7and 8 are formed by the discharge spaces 4a to 4d each having arectangular section whereby the laser beam 9a is to be amplified.

In short, in the waveguide path type CO₂ laser apparatus according tothe Embodiment 30, the rectangular sections of the four discharge spaces4a to 4d are arranged in a square shape, and the turn-back reflectionmirrors 7 and 8 are used, whereby the laser beam 9a can be amplifiedwithin the respective discharge spaces 4a to 4d, and the thus amplifiedlaser beam 9a can be handled solidly as one laser beam. Thus, theapparatus can be miniaturized, and the ceramic plate as a material fordielectrics 10 and 20 can be divided every unit U1 to U4 for use, thusreducing the cost.

EMBODIMENT 31

FIG. 41 is a sectional view showing a waveguide path type CO₂ laserapparatus according to Embodiment 30 of the present invention. FIG. 42is a perspective view showing a beam path of a laser beam shown in FIG.41.

In the Embodiment 30, four units U1 to U4 are arranged so that therectangular sections of the respective discharge spaces 4a to 4d are inthe square shape, whereas in the Embodiment 31, five units U1 to U5 areused, and rectangular sections of the discharge spaces 4a to 4e arearranged in a pentagon shape.

The operation of the Embodiment 31 is similar to that of the Embodiment30 but the beam path of the laser beam 9a is a beam path shown at thearrow in FIG. 42 unlike the case of the Embodiment 30. The operation andeffects are similar to those of the case of the Embodiment 30.

EMBODIMENT 32

FIG. 43 is a sectional view showing a waveguide path type CO₂ laserapparatus according to Embodiment 32 of the present invention. FIG. 44is a perspective view showing a beam path of a laser beam shown in FIG.45.

In the Embodiment 32, six units U1 to U6 are used, and rectangularsections of the discharge spaces 4a to 4f are arranged in a hexagonshape. The beam path of the laser beam 9a is a beam path shown at thearrow in FIG. 45, and the similar operation and effects are obtained.

That is, the Embodiments 30, 31 and 32 are characterized in that aplurality of discharge spaces each having a rectangular section arearranged in a polygon shape in section, the laser beam 9a is turned backand reflected by the turn-back type reflection mirrors 7 and 8 toreciprocate it plural times, and the laser beam to be turned back andreflected passes through all the discharge spaces and are amplifiedwhereby it can be handled as a single beam path. Accordingly, thedischarge spaces are provided in a the number which can be arranged in apolygon shape and the number is not limited.

EMBODIMENT 33

FIG. 46 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to Embodiment 33 of the presentinvention. FIG. 47 is a perspective view showing a beam path of a laserbeam shown in FIG. 46.

In this Embodiment 33, rectangular sections of four discharge spaces 4ato 4d are arranged at equal intervals about a point of intersection oftwo linear symmetrical axes L1 and L2 intersecting perpendicularly toeach other.

With this construction, there is obtained a beam path of a laser beam 9aindicated at the arrow in FIG. 47. Accordingly, the operation andeffects similar to the case of the Embodiment 30 are obtained. Thelinear symmetrical axes L1 and L2 mean the fact similar to thatmentioned in connection with the Embodiment 30 (FIG. 40).

EMBODIMENT 34

FIG. 48 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to Embodiment 34 of the presentinvention.

In the Embodiment 33, the rectangular sections of the four dischargespaces 4a to 4d are arranged at equal intervals in the radial direction,whereas in this Embodiment 34, rectangular sections of five dischargespaces 4a to 4e are radially arranged at equal intervals. A beam path ofa laser beam obtained in this case is similar to that shown in FIG. 42.Accordingly, the similar operation and effects are obtained.

EMBODIMENT 35

FIG. 49 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to Embodiment 35 of the presentinvention.

In this Embodiment 35, rectangular sections of six discharge spaces 4ato 4f are radially arranged at equal intervals. Accordingly, also inthis case, the similar operation and effects are obtained.

While in the aforementioned Embodiments 33 to 35, the case has beendescribed in which four to six discharge spaces are radially arranged,it is to be noted that the number of the discharge spaces is not limitedbut rectangular sections of a plurality of discharge spaces may beradially arranged so that at least two linear symmetrical axes or moremay be obtained.

EMBODIMENT 36

FIG. 50 is a perspective view of a laser apparatus according toEmbodiment 36 of the present invention. The fundamental structure of theEmbodiment 36 is similar to that of the aforementioned Embodiment 30.However, in the Embodiment 36, rod-like metal electrodes 1a, 2a and 1b,2b are used in place of the flat plate-like metal electrodes 1, 2 in theEmbodiment 30.

That is, in the Embodiment 36, a pair of flat plate-like dielectricplates 10, 20 are opposed to each other form one unit. Such four unitsU1 to U4 are arranged so that rectangular sections of discharge spaces4a to 4d assume a square shape, and the four rod-like metal electrodes1a, 2a and 1b, 2b are arranged in the direction of and along the majorsides on both sides of the discharge spaces 4a to 4d.

With such a construction, the discharge is caused in the direction ofthe major side of the respective discharge spaces 4a to 4d each having arectangular section. Also in this case, the dielectric plates 10 and 20are being cooled, whereby the laser gas is cooled through the dielectricplates 10 and 20. Accordingly, the effect similar to that of theEmbodiment 30 is obtained.

While in the Embodiment 36, the case has been described in which fourdischarge spaces 4a to 4d are present, it is to be noted that the numberthereof is not limited.

EMBODIMENT 37

FIG. 51 is a perspective view of a solid laser apparatus according toEmbodiment 37 of the present invention.

The solid laser apparatus according to the Embodiment 37 is a YAG slablaser apparatus in which a slab type solid laser medium is used as alaser light excitation medium, the laser medium is comprised of YAG(Y_(3-k) N_(dx) Al₅ O₁₂) and the shape thereof is slab-like.

In the figure, reference numerals 41a to 41d represent four solidelements comprised of a YAG crystal having a slab shape. These solidelement 41a to 41d are arranged in a square shape in section.

Reference numerals 42a to 42e represent light sources for exciting thesolid elements 41a to 41d. These light sources 42a to 42e consist ofexternal light sources 42a to 42d arranged along the lengthwise of thesurfaces of the solid elements 41a to 41d, and an internal light source42e arranged in the center portion of a space portion surround by thesolid elements 41a to 41d.

Reference numerals 3a to 3e designate power sources for lighting thelight sources 42a to 42e, and reference numerals 7 and 8 designatereflection mirrors of the turn-back reflection type. These reflectionmirrors 7 and 8 are arranged with the beam turn-back directionsdifferentiated at 90° similar to the case of the aforementionedEmbodiment 30. Reference numeral 83 designates a laser beam emittingport, and numeral 9 designates a laser beam emitted from the laser beamemitting port 83.

The operation of the Embodiment 37 is substantially similar to that ofthe Embodiment 30. The laser beams amplified by the four solid elements41a to 41d provided in the YAG slab laser apparatus are turned back andreflected plural times by the reflection mirrors 7 and 8 to thereby forma solidly joined beam path.

Accordingly, one laser beam 9 is emitted from the laser beam emittingport 83. The function of the reflection mirrors 7 and 8 is exactly thesame as that of the Embodiment 30.

While in the Embodiment 37, four solid elements 41a to 41d are arrangedin a square shape in section, it is to be noted that the number of thesolid elements is not limited but the number of solid elements capableof being arranged in a polygonal shape in section will suffice. In anycase, the effect similar to that of the Embodiment 30 is obtained, and ahigher output of laser can be attained.

EMBODIMENT 38

FIG. 52 is a view showing the arrangement of a solid laser medium of asolid laser apparatus according to Embodiment 38 of the presentinvention.

In the Embodiment 38, four solid element 41a to 41d are arranged in across shape in section so as to obtain at least two linear symmetricalaxes L1 and L2. Also in this case, the similar effects are obtained.

EMBODIMENT 39

FIG. 53 is a view showing the arrangement of a solid laser medium of asolid laser apparatus according to Embodiment 39 of the presentinvention.

In the Embodiment 39, six solid elements 41a to 41f are used. Thesesolid elements 41a to 41f are radially arranged at equal intervals abouta point of intersection of these two linear symmetrical axes L1 and L2.The effects similar to that of the Embodiment 37 are obtained.

EMBODIMENT 40

FIG. 54 is a perspective view of a solid laser apparatus according toEmbodiment 40 of the present invention.

In the Embodiment 40, the flat plate-like solid elements 41a to 41d inthe Embodiment 37 are replaced by rod-like solid elements 51a to 51d.Other structures are similar to those of the Embodiment 37, andaccordingly, the operation and effects are similar.

It is to be noted that also in the Embodiment 39, the number of solidelements is not limited.

EMBODIMENT 41

FIG. 55 is a perspective view showing essential parts of a waveguidepath type CO₂ laser apparatus according to Embodiment 41 of the presentinvention.

In the waveguide path type CO₂ laser apparatus in the aforementionedEmbodiments 30 to 33, a plurality of rectangular discharge spaces areused, whereas in the Embodiment 41, a single discharge space 4 is formedin a circular shape in section. That is, in the Embodiment 41, metalelectrodes 1, 2 and dielectrics 10, 20 are in the form of a circularpipe, which are arranged in a coaxial multiple tubular fashion. Thereby,a single circular discharge space 4 is formed between the circulardielectrics 10 and 20, and reflection mirrors 7 and 8 similar to thoseof the aforementioned Embodiments 30 to 33. The similar effects areobtained.

EMBODIMENT 42

FIG. 56 is a perspective view showing essential parts of a waveguidepath type CO₂ laser apparatus according to the Embodiment 42 of thepresent invention.

In this Embodiment 42, a single discharge space 4 in the Embodiment 40is formed into an oval shape. Accordingly, the similar effect isobtained even in this case.

EMBODIMENT 43

FIG. 57 is a perspective view of a solid laser apparatus according toEmbodiment 43 of the present invention. In the above-describedEmbodiments 37 to 39, a solid laser apparatus having a plurality ofslab-shaped solid elements is described whereas in the Embodiment 43, asingle solid element 41 is formed into a circular tubular configuration.Other structures are similar to those of the Embodiment 37 (FIG. 51).Even a solid laser apparatus having a single circular and annular solidelement 41, the similar effects are obtained.

EMBODIMENT 44

FIG. 58 is a perspective view showing essential parts of a solid laserapparatus according to Embodiment 44 of the present invention.

In the Embodiment 44, a single discharge space 4 in the Embodiment 42 isformed into an oval shape. Accordingly, also in this case, the similareffects are obtained.

EMBODIMENT 45

FIG. 59 is a sectional view showing essential parts of a waveguide pathtype CO₂ laser apparatus according to Embodiment 45 of the presentinvention. The fundamental configuration of Embodiment 45 is similar tothat of the prior art example (FIG. 69).

In this Embodiment 45, dielectric plates 10 and 20 are formed from twokinds of dielectric layers 611, 612 and 621, 622 which are different indielectric constant from each other.

The two kinds of dielectric layers 611, 612 and 621, 622 may beconnected by electric insulative adhesive layers or may be connected byconductive materials. In this case, on the side of metal electrodes 1and 2, there are provided high dielectric-constant layers 611, 621formed of a high dielectric-constant material (dielectric constantε_(H)), and on the side of the waveguide path (discharge side), thereare provided low dielectric-constant layers 611, 622 formed of a lowdielectric-constant material (dielectric constant: ε_(L)).

A thickness (tH) of the high dielectric-constant layers 611, 621 is setto be thicker (tH>tL) than a thickness (tL) of the lowdielectric-constant layers 612, 622.

The operation of the Embodiment 45 is basically similar to the case ofthe conventional apparatus shown in FIG. 69. When an alternating voltageis applied to the metal electrodes 1 and 2, laser excitation is effectedby the discharge occurred in the discharge space 4. Since the lowdielectric-constant layers 612, 622 are formed on the waveguide pathsurface on which laser beam is reflected, the propagation loss of lightcan be minimized as will be understood from the above-described formula(1).

Next, the electric characteristics will be mentioned. When a sine wavevoltage is applied, an energy: discharge power Wd charged into thedischarge space 4 is given by the following formula (5): ##EQU2##wherein f represents the power source frequency, V* represents thedischarge voltage, and Vop represents the crest value of the appliedvoltage. Cd represents the electrostatic capacity of the dielectrics 10and 20. In the case where the dielectrics 10 and 20 are formed of acomposite material (the electrostatic capacity: (C_(H),C_(L)) as shownin FIG. 59, the electrostatic capacity is as follows: ##EQU3## From thearea S and the thickness t of the dielectric plates 10 and 20 and thespecific permeability ε, the electrostatic capacity C is as follows:##EQU4## So, if the thickness (t_(H)) of the high dielectric-constantlayers 611 and 621 is set to be sufficiently thicker (t_(H) >t_(L)) thanthe thickness (t_(L)) of the low dielectric constant layers 612 and 622,

    C.sub.L >>C.sub.H                                          (8)

is given from the formula (7).

It is understood from the formulae (6) and (8) that the effectiveelectrostatic capacity Ceff substantially accords with the capacityC_(H) of the high dielectric-constant layers 611 and 621 (C_(tH)=C_(tL)).

That is, even if the low dielectric-constant layers 612, 622 are platedon the high dielectric-constant layers 611, 621, if its thicknessincreases, the electric characteristics remain unchanged, and thesimilar discharge characteristics are obtained.

In the waveguide path type laser apparatus, the functions required bythe dielectrics 10 and 20, that is, the electric performance related tothe discharge and the optical performance related to the lightpropagation are shared with the dielectrics 10 and 20 layers. Therefore,the low dielectric-constant materials which are hard to be sintered thatcould not be used heretofore for the apparatus of this kind and thematerials from which thick plates could not be fabricated due to theweak thermal distortion are rendered possible to use to extremely widenan allowance of materials to be used.

EMBODIMENT 46

In the aforementioned Embodiment 45, the case has been disclosed inwhich the low dielectric-constant layers 612, 622 are made to besufficiently thin. In the case where the power source frequency to beused is sufficiently high, even an extremely low voltage a high powercan be used as will be apparent from the aforementioned formula (5). Inthis case, not much electric characteristics are not required for thedielectric plates 10 and 20. In the case of such conditions asdescribed, it is not necessary to make the low dielectric-constantlayers 612, 622 sufficiently thinner than the high dielectric-constantlayers 611, 621 but as shown in FIG. 60, the thickness of the highdielectric-constant layers 611, 621 may be made to be substantiallyequal to that of the low dielectric-constant layers 612, 622, or therelationship of the thickness therebetween may be reversed.

EMBODIMENT 47

In the Embodiments 45 and 46, the case has been described in which twodielectric materials are superimposed for use. However, as shown in FIG.61, the low dielectric-constant layers 612, 622 may be formed on thesurfaces of the high dielectric-constant layers 611, 621 by flamespraying. Of course, the low dielectric-constant materials may be coatedby processes other than the flame spraying to obtain the similareffects.

EMBODIMENT 48

In the case of a carbon dioxide gas laser of wavelength 10.6 μm,preferable materials used for the low dielectric-constant layers 612,622 are BeO or AIN.

EMBODIMENT 49

In the Embodiments 45 to 48, the CO₂ laser apparatus has been described,but of course it can be applied to the waveguide path type laserapparatus.

EMBODIMENT 50

FIG. 62 is a sectional view of a laser apparatus according to Embodiment50 of the present invention. The fundamental structure of Embodiment 50is similar to that of prior art example (FIG. 69). This sectional viewis viewed from the direction of an optical axis but it can be likewiseviewed from the direction intersecting perpendicularly to the opticalaxis.

In FIG. 62, reference numerals 511 to 513 and 521 to 524 areindividually divided metal electrodes. In these metal electrodes 1,voltages different in polarity or voltage phase are applied to metalelectrodes 511 and 512, 512 and 513, 521 and 522, and 522 and 523adjacent to each other, and voltages of the same phase are applied tometal electrodes 511 and 521, 512 and 522, and 513 and 523 opposed tothe discharge space 4.

In order to enhance the cooling of a laser gas, electrically floatedcooling pipes 141 to 143 and 144 to 146 are respectively disposedbetween the metal electrodes 511, 512 and 513, and between 521, 522 and523. These are cooled along with a feeder pipe.

The laser gas is cooled by the cooling pipes 141 to 146 through thedielectric plates 10 and 20. Further, in order to prevent the dischargebreakage other than the discharge space 4, the metal electrodes 511 to514 and 521 to 524 are molded by the dielectrics 110 and 120. That is,when alternating voltages are applied to the metal electrodes 511 to 514and 521 to 524, the discharge lengthwise of the discharge space 4 occursbetween the adjacent metal electrodes (for example, 511 and 512) whichare different in polarity. At that time, the creeping-discharge or thelike sometimes occurs in portions other than the discharge space 4.Therefore, the metal electrodes 511 to 514 and 521 to 524 are molded bythe dielectrics 110 and 120. For materials of the dielectrics 110 and120 used, properties such that insulation is excellent (voltageresistance: 5 kV/mm or more); an organic material less generates; and aflexibility after hardened is provided. Therefore, fillers of a siliconfamily are most suitable for use.

According to the configuration of the Embodiment 50, it is extremelyeasy to set the effective gas length of the discharge to be long aspreviously mentioned.

That is, the object is achieved by setting the spacing between the metalelectrodes 511 to 514 and 521 to 524 adjacent to each other to be large.Since the spacing between the metal electrodes can be suitably set, theoptimization can be provided according to the power source frequency tobe used. That is, in case of the low power source frequency, the spacingbetween the metal electrodes 1 may be set long. However, when thespacing between the metal electrodes 1 becomes long to some extent, thecooling efficiency of gas lowers, but the cooling pipes 141 to 146 arearranged between the metal electrodes adjacent to each other as shown inFIG. 62, thus being more effective. It is to be noted that the coolingpipes 141 to 146 may be electrically floated or installed as previouslymentioned.

FIGS. 63 and 64 show the results obtained by investigating thedependability of the power source frequency of the laser output whereinthe spacings between the metal electrodes 511 to 514 and 521 to 524 are5 mm and 15 mm, respectively, under the condition that the gas length is2 mm. In the case of 5 mm (FIG. 63), the excitation efficiencies of 150MHz and 13.56 MHz are nearly the same, and in the case of 15 mm (FIG.64), the excitation efficiency of 100 KHz is also nearly the same. Ithas been found that the laser excitation efficiency in a low frequencyregion has been improved.

EMBODIMENT 51

While in the Embodiment 50, the case has been described where thevoltages of the same phase are applied to the metal electrodes 511 and521, 512 and 522, and 513 and 523 opposed to the discharge space 4, itis to be noted that one of opposed metal electrodes 525 need not bedivided as shown in FIG. 65 but it may be installed or electricallyfloated.

EMBODIMENT 52

As shown in FIG. 66, when a voltage different in phase is applied to apart (in the figure, 511 and 521) of the metal electrodes opposed to thedischarge space 4, the discharge occurs between the metal electrodes 511and 521 with an extremely low voltage to facilitate the start of otherdischarges, and enable the enhancement of stability of the discharge.This may result from the preliminary ionization effect of the spacecaused by charged particles or ultraviolet rays generated from thedischarge 444. Even in the case where either the metal electrode 511 or521 is grounded, the similar effects are obtained.

EMBODIMENT 53

In this Embodiment 53, a polyphase power source 300 is used as shown inFIG. 67 to vary a movement of voltage to be applied to the metalelectrodes adjacent to each other. In this way, the effects similar tothose mentioned in connection with the Embodiments 50 to 53 areobtained. While here, an example of four-phase power source has beenshown, it is to be noted that three-phase or other polyphase powersources may be used of course.

EMBODIMENT 54

In this Embodiment, a plurality of power sources 310, 311 and 312 areused as shown in FIG. 68. Also in this case, the similar effects areobtained.

EMBODIMENT 55

While in the Embodiments 50 to 54, the CO₂ laser apparatus has beendescribed, it is to be noted that other gas lasers such as a CO laserwhich require for excitation with low energy can be also employed.

It is to be noted that the present invention is not limited to theembodiments described above and many changes and modifications can bemade thereto without departing from the spirit and scope of theinvention as set forth herein.

What is claimed is:
 1. A laser apparatus comprising: means defining adischarge space having a doughnut-like annular section comprising anouter pipe and an inner pipe coaxially disposed, an inner periphery ofsaid outer pipe and an outer periphery of said inner pipe being utilizedas waveguide paths for a laser beam that is output by said dischargespace in a direction intersecting perpendicularly to said annularsection; andtwo or more electrodes for applying an alternating voltagedisposed in the outer periphery of said outer pipe, wherein said outerpipe is formed from a dielectric.
 2. A laser apparatus comprising: meansdefining a discharge space having a doughnut-like annular sectioncomprising an outer pipe and an inner pipe coaxially disposed, an innerperiphery of said outer pipe and an outer periphery of said inner pipebeing utilized as waveguide paths for a laser beam that is output bysaid discharge space in a direction intersecting perpendicularly to saidannular section; andtwo or more electrodes for applying an alternatingvoltage juxtaposed in the direction of outputting a laser beam in theouter periphery of said outer pipe, wherein said outer pipe is formedfrom a dielectric.
 3. A laser apparatus according to claim 1 or 2,wherein said inner pipe is formed from a conductor.
 4. A laser apparatusaccording to claim 1 or 2, wherein said inner pipe is formed from adielectric.
 5. A laser apparatus according to claim 1 or 2, wherein saidinner pipe is constituted by coating a dielectric layer on the outerperiphery of a tubular body formed from a conductor.
 6. A laserapparatus according to claim 5, wherein said tubular body is grounded.7. A laser apparatus according to claim 1 or 2, further comprising, inthe outer periphery of said outer pipe, electrically floated conductivemembers alternately disposed with said electrodes for applying avoltage, said electrodes and said conductive members being cooled.
 8. Alaser apparatus according to either of claims 1 to 2, wherein the innerpipe is cooled.
 9. A laser apparatus according to either of claims 1 or2, further comprising a polyphase alternating power source having morethan three phases.
 10. A laser apparatus according to either of claims 1or 2, wherein said electrodes are adjacent to each other, andalternating voltages different in phase are applied to said electrodes.11. A laser apparatus according to claim 10, further comprising anelectrically floated or grounded cooling pipe disposed betweenelectrodes adjacent to each other.